A bridge or elevated roadway for example may be constructed of a series of separate structural slabs placed end-to-end. It is necessary to leave gaps between the slabs to accommodate thermal expansion and contraction. Normal practice is to bridge these gaps by means of a joint that can provide an effective seal between the slabs as well as permitting relative movement thereof. Many different forms of expansion joint have been devised with the aim of serving this function. Generally, an expansion joint of this type comprises a pair of channel-shaped steel retainers that are secured to the roadway sections to be joined with their channels facing one another, and an elongate rubber seal member, marginal portions of which are installed in the respective retainers. Typically, the seal is generally V-shaped in cross-section so that movement of the two roadway sections relative to one another will be accommodated by variations in the angle of the V.
Expansion joints are of course subject to severe service conditions. The seal must be capable of withstanding not only year-round weather and temperature changes, but also the effects of road salt, grit and other debris. When a particular joint is in an open condition, stones, rocks and other debris can accumulate in the seal and generally will not be dislodged naturally. When the gap closes due to temperature change, the debris can damage the seal or exert forces that tend to tear the seal out of one of its retainers.